It is our objective to carry out detailed structure analyses of enzymes by the established techniques of x-ray crystallography. We propose to continue studies of the flavoprotein enzymes involved in biological oxidations, already initiated by the determination of the crystal structures of all three oxidation states of clostridial flavodoxin. Our choice of enzymes appropriate for structure analysis has been determined by the desire to 1) elucidate enzyme-substrate interactions, 2) understand the changes of structure accompanying oxidation or reduction of the prosthetic group, 3) correlate the structure with biological reactivity and physical properties. The results obtained with flavodoxin from C1. MP, a prototype flavoprotein dehydrogenase, have led to a description of the flavin-protein interactions, shown subtle changes of structure upon reduction of the flavin, and revealed unexpected species variations in the active center, along with conservation of an elemental dehydrogenase structure. The flavodoxin from another species, Anacystis nidulans, has been crystallized and its structure will be compared with that of clostridial flavodoxin. Conformations of the known flavodoxins, obtained after refinement, are being utilized to simplify solution of this new structure. We intend to extend structural analyses to larger flavoproteins such as those for which the flavodoxins (or similar electron carriers) are substrates, viz. ferredoxin-NADP-reductase or adrenodoxin reductase. Ferredoxin-NADP-reductase has been crystallized in this and other laboratories; we have also crystallized a complex containing both the reductase and ferredoxin. The spectral properties of the above proteins will be studied, both in solution and crystalline states. It will be our aim to compare the properties of the crystalline E-S "models" with deductions from kinetic and spectroscopic studies in solution. BIBLIOGRAPHIC REFERENCES: Ludwig, M.L., Burnett, R.M., Darling, G.D., Jordan, S.R., Kendall, D.S., and Smith, W.W. "Flavin Mononucleotide-Protein Interactions in Flavodoxin from Clastridium MP", in 4th Steenbock Symposium (Sundaralingam, M. and Rao, S.T., Eds.) held in Madison, Wisconsin, June 1974. Symposium title: Structure and Conformation of Nucleic Acids and Protein-Nucleic Acid I (Text Truncated - Exceeds Capacity)